CBR: Constant Bitrate
With CBR, every second of audio gets exactly the same number of bits - a 192 kbps CBR file uses 192 kbps during silence and during a drum fill alike. The upside is total predictability: file size is exactly bitrate x duration, seeking is precise, and every player and streaming server handles it flawlessly. The downside is inefficiency - quiet passages waste bits while dense passages may be starved.
VBR: Variable Bitrate
VBR targets a quality level instead of a rate, letting the bitrate float moment to moment (an MP3 frame can range from 32 to 320 kbps). The result is typically 10-20% smaller files at equal quality, or better quality at equal size. Drawbacks are minor but real: duration estimates can display incorrectly in old players, seeking can be less precise, and a handful of legacy devices and platforms mishandle VBR streams.
Which Should You Use?
- Music libraries for modern devices: VBR - best quality-per-megabyte.
- Podcasts: CBR is the long-standing recommendation, because some podcast apps and streaming endpoints still misbehave with VBR (skipping, wrong durations). See podcast bitrate advice.
- Maximum compatibility with old hardware: CBR.
- Absolute peace of mind: 320 kbps CBR - the ceiling of MP3, at the cost of larger files.
CBR and VBR on mp3.now
mp3.now encodes at the constant bitrate you select, keeping output predictable and universally compatible. Pick your rate on any converter page or with the bitrate changer: upload, choose the bitrate option, click Convert, download. If you received a VBR file that a device refuses to play, converting it through a fixed-bitrate pass normalises it to CBR.
How to Tell Which One a File Uses
Most desktop players reveal it in the file-properties or codec-information panel: a fixed figure like "192 kbps" indicates CBR, while a fluctuating readout or an explicit "VBR" label indicates variable bitrate. There is also a quick arithmetic check - divide file size by duration. If a 4-minute file is almost exactly 5.8 MB, that is 192 kbps CBR (bitrate x duration holds precisely for CBR); an odd, in-between figure suggests VBR. You may also meet ABR (average bitrate), a halfway mode that varies frame-to-frame while steering toward a target average - treat it like VBR for compatibility purposes. None of this affects everyday listening; it matters when diagnosing wrong durations in a player, preparing podcast files, or working with equipment that documents CBR-only support.